No abstract

The soil microbiome is the key player regulating phosphorus cycling processes. Identifying phosphate-solubilizing bacteria and utilizing them for release of recalcitrant phosphate that is bound to rocks or minerals have implications for improving crop nutrient acquisition and crop productivity.

A plasmid, pTA163, in Escherichia coli contained an approximately 34-kb gene fragment from Pseudomonas putida JYR-1 that included the genes responsible for the metabolism of trans-anethole to protocatechuic acid. Three Tn5-disrupted open reading frame 10 (ORF 10) mutants of plasmid pTA163 lost their abilities to catalyze trans-anethole. Heterologously expressed ORF 10 (1,047 nucleotides [nt]) under a T7 promoter in E. coli catalyzed oxidative cleavage of a propenyl group of trans-anethole to an aldehyde group, resulting in the production of para-anisaldehyde, and this gene was designated tao (trans-anethole oxygenase). The deduced amino acid sequence of TAO had the highest identity (34%) to a hypothetical protein of Agrobacterium vitis S4 and likely contained a flavin-binding site. Preferred incorporation of an oxygen molecule from water into p-anisaldehyde using 18 Olabeling experiments indicated stereo preference of TAO for hydrolysis of the epoxide group. Interestingly, unlike the narrow substrate range of isoeugenol monooxygenase from Pseudomonas putida IE27 and Pseudomonas nitroreducens Jin1, TAO from P. putida JYR-1 catalyzed isoeugenol, O-methyl isoeugenol, and isosafrole, all of which contain the 2-propenyl functional group on the aromatic ring structure. Addition of NAD(P)H to the ultrafiltered cell extracts of E. coli (pTA163) increased the activity of TAO. Due to the relaxed substrate range of TAO, it may be utilized for the production of various fragrance compounds from plant phenylpropanoids in the future. Bacterial metabolism as a means of producing value-added compounds from natural resources has been given much attention as an alternative method to replace conventional chemical syntheses (21,27). If natural resources can be continuously supplied as the starting materials, biotransformation employing bacterial systems may become practical from the points of view of sustainability and applicability. One of the major groups of natural compounds targeted for the production of value-added compounds includes the group of chemicals that occur in plant phenylpropanoid pathways, which are involved in the production of lignin, flavonoids, anthocyanins, etc. (5, 16-19). For example, isoeugenol, eugenol, and ferulic acid produced by the phenylpropanoid pathway have often been attempted as the starting materials to produce vanillin, one of the most extensively used aromatic flavor compounds (25-27, 32).trans-Anethole (p-methoxy propenylbenzene), the major component present in the essential oils of anise, fennel, and star anise, is also a type of phenylpropanoid compound formed by terpene synthesis in plants (10). trans-Anethole is used commercially as a flavor substance in baked goods, candy, ice cream, chewing gum, and alcoholic beverages (21). However, there have been few research reports regarding its metabolism (8,12,21,22,31). Indeed, to date, the only two bacterial strains isolated that are known to use trans-anethole as a sole carbon source are Arthrobacter sp. strain TA13 and Pseudomonas putida JYR-1 ...